These two (un)lucky songs entered the chart at #6 only to never be seen again after that:

Walters and Kazha – The War Is Not Over (week 18 2005)Danielle Paris – I Can't Stand It (week 52 2005)

Note that the rules of my chart (how a song's score is computed) make it unlikely that drops like these happen even for songs I completely stop listening to. Only four other songs have entered lower in the top 10 and dropped out the week after.